title: Poor agreement between respiratory variations in pulse oximetry photoplethysmographic waveform amplitude and pulse pressure in intensive care unit patients.
abstract: BACKGROUND
  To identify fluid responsiveness, a correlation between respiratory variations in pulse pressure (DeltaPP) and respiratory variations in pulse oximetry photoplethysmographic waveform amplitude (DeltaPOP) in mechanically ventilated patients has been demonstrated. To evaluate the agreement between the two methods, knowledge about the repeatability of the methods is imperative. However, no such data exist. Based on knowledge of slow oscillation in skin blood flow, the authors hypothesized that the variability of DeltaPOP would be larger than that of DeltaPP when calculations were performed continuously over a long recording period.
  
  
  METHODS
  Respiration, continuous invasive blood pressure, pulse oximetry, and skin microcirculation were recorded in 14 mechanically ventilated intensive care unit patients. No intravenous fluid challenges were given, and no other interventions were performed during the measurements. Seventy consecutive comparisons between DeltaPP and DeltaPOP were calculated for each of the 14 patients.
  
  
  RESULTS
  For all patients, DeltaPOP was 13.7 +/- 5.8% and DeltaPP was 5.8 +/- 2.6% (P < 0.001). There was a larger intraindividual (8.94 vs. 1.29; P < 0.001) and interindividual (26.01 vs. 5.57; P < 0.001) variance of DeltaPOP than of DeltaPP. In six patients, there was no significant correlation between DeltaPP and DeltaPOP. A Bland-Altman plot showed poor agreement between the two methods.
  
  
  CONCLUSIONS
  A large variability of DeltaPOP and a poor agreement between DeltaPP and DeltaPOP limits DeltaPOP as a tool for evaluation of fluid responsiveness in intensive care unit patients. This is in contrast to DeltaPP, which shows a small variability.
authors.affiliation: Department of Anesthesiology, Ulleval University Hospital, Oslo, Norway. s.a.landsverk@medisin.uio.no
authors.forename: Svein Aslak
authors.initials: SA
authors.lastname: Landsverk
authors.forename: Lars O
authors.initials: LO
authors.lastname: Hoiseth
authors.forename: Per
authors.initials: P
authors.lastname: Kvandal
authors.forename: Jonny
authors.initials: J
authors.lastname: Hisdal
authors.forename: Oivind
authors.initials: O
authors.lastname: Skare
authors.forename: Knut A
authors.initials: KA
authors.lastname: Kirkeboen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001794:Blood Pressure / Q000502:physiology*; D005260:Female; D006801:Humans; D007362:Intensive Care Units / Q000592:standards*; D008297:Male; D008875:Middle Aged; D010092:Oximetry / Q000379:methods / Q000592:standards*; D017156:Photoplethysmography / Q000379:methods / Q000592:standards; D015203:Reproducibility of Results; D012121:Respiration, Artificial / Q000379:methods / Q000592:standards; D015656:Respiratory Mechanics / Q000502:physiology*